The effects of chronic insulin administration on the metabolism of isolated adipose cells and muscle were studied. Adipose cells from 2 and 6 week insulin-treated and control rats, fed either chow or chow plus sucrose, were prepared and insulin binding, 3-0-methylglucose transport, glucose metabolism, and lipolysis were measured at various insulin concentrations. After 2 weeks of treatment, adipose cell size, and basal glucose transport and metabolism are unaltered, but insulin-stimulated glucose transport and metabolism are increased two- to three-fold when cells are incubated in either 0.1 mM glucose (transport rate-limiting) or 10 mM glucose (maximum glucose metabolism). Insulin binding is increased 30 to 50%, but no shift in the insulin dose-response curve for glucose transport or metabolism occurs. After 6 weeks of treatment, the effects of hyperinsulinemia persist and are superimposed on the changes in cell function which occur with increasing cell size in aging rats. No changes in lipolysis could be measured. Finally, no changes in glucose metabolism occur in incubated soleus muscle strips. These results suggest that chronic hyperinsulinemia increases insulin binding and the capacity of adipose cells, but not muscle, to metabolize glucose without changing the cells' sensitivity to insulin. Increased glucose utilization results from both increased transport and increased intracellular glucose metabolism.